Two things I would consider...

1. Thats a real nice turbo fan you got there. Those things on even speed #2 can be a little violent on such young plants.

When blowing on them, you just want to wisp them with air...not make them fight. One thing it could be, is the stem is not rebuilding at the stress point.

How fast is the fan blowing on them????

Also, NL #2 looks, from the pic, like it might have the same problem going on.

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2. That 400W HPS looks awfully close to be on such young tender plants. What is the temperature at plant leaf top level?

I dont think the growth is any slower than it should be...growth rate will accelerate as the plant learns to live.

Mine were the same at week one....

If you look at the plants on the pic, the little ones are all day 10 - 14. They grew up to be real nice....

Let us know about the fan and the temp..... Maybe we can figure it out.....